Radio receiver



May25, 1937. f E KLoTZ 2,081,277

RADIO RECEIVER Filed May '7, 1934 50i/ND KEF/900065.?

assigner toA Tlefunken Gesellschaft'fr Dra l'ose'llegraphie,

m. b. H., Berlin, Germa Germany a corporation off Application May 7,1934, Serial No. 724,261 In Germany May 11, 1933 2 Claims,

This invention relates to radio receiver sets with intermediatefrequency amplification useful for phonograph record reproduction. Theobject of the invention is to provide a broadcast receiver which may beemployed at will for broadcast reception and for the reproduction ofphonograph records, and which operates upon the principle of heterodynereception.

It is known in the prior art to provide ways and means whereby the radiofrequency amplifier tubes used during actual broadcast reception arerendered non-responsive and non-operative when changing the set to thereproduction of phonograph records in order to make conditions suchthat, especially during the playing of low passages on a phonographrecord, the effect of signals coming in from powerful sending stationsupon the reproducer may be avoided.

According to this invention a heterodyne receiver set is so designedthat'when changing it over to phonograph record reproduction, theregenerative means of the local heterodyne oscillator are renderedinoperative. Furthermore, in order to preclude all chances of anypossible existent powerful transmitter whose sending wave is close tothe intermediate frequency wave, from being received and being furtheramplified in the intermediate frequency cascade, it is also advisable todetune the input circuits at the same time the local oscillator circuitis changed. This may be accomplished by tuning part of the input circuitto short wave reception and another part to long wave reception.

One exemplified embodiment of the invention is illustrated in thedrawing. Referring to the drawing, A denotes the antenna. The latter isin coupling relation with the input circuit of a so-called hexode (i. e.amplifier equipped with four grid electrodes). Upon the grid I closestto the cathode is impressed the input potential. The second grid 2 actsas a screen grid. The third grid 3 serves for the generation of theheterodyne frequency, and is connected to an oscillation circuit -Otuned to the heterodyne frequency. In the external circuit of the fourthgrid 4 is included the regeneration or tickler coil 5 coupled with thecoil 6 of the tuned circuit O The plate circuit is coupled with theintermediate frequency amplifier cascade by the transformer 8. Accordingto this invention, by the aid of the ground switch E the fourth gridwhich contains the tickler coil in its external circuit, is grounded andin this manner the mixer tube M is prevented from oscillating so thatheterodyning of the incoming waves and thus conversion into theintermediate frequency may not be brought about. It will be seen thatwhen grid 4 is grounded, its potential remains constant and therefore novariable current ows through coil 5 to cause circuit O to oscillate, theoscillator portion of the tube no longer functioning to produce thelocal oscillation frequency. However, in this condition the tube maystill act as a triode amplifier to amplify currents of the intermediatefrequency which may be received on the antenna and impressed on grid I,the steady potentials of grids 3 and 4 not destroying the amplifyingproperties of the tube.

Moreover, the input circuits K--I and K-2 which are to be tuned to theincoming waves by the variable condensers shown and which are designedso as to be changed to short-wave and long-wave reception as by theswitches I and 9, are arranged for different wave length ranges in orderthat the action of powerful transmitters whose wave is, for instance,close to that of the intermediate frequency, may be avoided.

The socket G for plugging in the electric pickup I is united by means ofa switch S with the input circuit of the first audio frequency tube (notshown). The switches S and E are mechanically interconnected bypositively acting means indicated diagrammatically by the dotted line B.It will be understood that when the switch S is closed for phonographreproduction, one of the switches, such as I of the grid circuit, willbe closed in its lower position to tune this circuit within the longwave band while at the same time the switch 9 will also be closed in itsupper position to tune the coil of the antenna circuit to a frequencywithin the short wave band. Under these conditions these two circuitsact very effectively as a lter to prevent any currents which may bepicked up by the antenna from a station transmitting on the intermediatefrequency from being transmitted to the grid I and amplified by tube Mand the intermediate frequency amplifier and thus interfering with thephonograph reproduction.

The tubes following the first intermediate frequency have been omittedbecause they are here unimportant.

What I claim is:

1. A radio phonograph device comprising in combination, the cascadeconnection of a first detector tube, an intermediate frequencyamplifier, a second detector, an audio frequency amplifier and a soundreproducer, said rst detector tube having a grid-cathode circuitincluding a tuning means and a switching device arranged to cause saidtuning means to tune. said circuit to either a long wave band or a shortwave band, an input circuit coupled to said grid-cathode circuit andincluding a second tuning means and a second switching device arrangedto cause said second tuning means to tune said input circuit to either along wave band or a short wave band, means for modu1ating.the currentwithin said detector tube at a local oscillation frequency, means forrendering said modulating means inoperative while one of said switchingdevices is adjusted for reception within the long wave band and theother of said switching devices is adjusted for reception within theshort Wave band, a phonograph pickup and a circuit including a switchingdevice connecting said pickup to said audio frequency amplifier.

2. 'I'he combination deiined in the preceding claim in which the meansfor modulating the detector tube current at the local oscillationfrequency includes two additional grids within said tube, a circuittuned to the local oscillation frequency connected to the first of saidgrids, a circuit connected to the second of said grids including afeedback connection to said last named circuit and means arranged toground said second grid to thereby render said modulating meansinoperative.

ERNST KLOTZ.

